xref: /dragonfly/sys/libkern/random.c (revision dc71b7ab)
1 /*-
2  * Copyright (c) 1992, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. Neither the name of the University nor the names of its contributors
14  *    may be used to endorse or promote products derived from this software
15  *    without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27  * SUCH DAMAGE.
28  *
29  *	@(#)random.c	8.1 (Berkeley) 6/10/93
30  * $FreeBSD: src/sys/libkern/random.c,v 1.7 1999/08/28 00:46:36 peter Exp $
31  * $DragonFly: src/sys/libkern/random.c,v 1.6 2006/09/03 18:52:29 dillon Exp $
32  */
33 
34 #include <sys/libkern.h>
35 
36 static u_long randseed = 1;
37 
38 void
skrandom(u_long seed)39 skrandom(u_long seed)
40 {
41 	randseed = seed;
42 }
43 
44 /*
45  * Pseudo-random number generator for randomizing the profiling clock,
46  * and whatever else we might use it for.  The result is uniform on
47  * [0, 2^31 - 1].
48  */
49 u_long
krandom(void)50 krandom(void)
51 {
52 	long x, hi, lo, t;
53 
54 	/*
55 	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
56 	 * From "Random number generators: good ones are hard to find",
57 	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
58 	 * October 1988, p. 1195.
59 	 */
60 	x = randseed;
61 	hi = x / 127773;
62 	lo = x % 127773;
63 	t = 16807 * lo - 2836 * hi;
64 	if (t <= 0)
65 		t += 0x7fffffff;
66 	randseed = t;
67 	return (t);
68 }
69